Cast coated paper and method of making the same



1952 J. v. ROBINSON ETAL 3,02

CAST COATED PAPER AND METHOD OF MAKING THE SAME Filed March 13, 1958 CASTING ROL L TENSION ROLL WINDE R ROL L JAMES V. ROBINSON, By EARL B. BROOKBANK, JR.

ATTORNEYs United States Patent Office 3,020,176 Patented Feb. .6, 1962 3,020,176 PAPER AND METHOD This invention relates to the production of high gloss cast surfaced mineral coated papers, and more particularly to agents which are effective in providing ready and complete release of such coated papers from a casting surface.

Various known methods of producingcast-surfaced mineral-coated papers are similar in that a wetand plastic coated paper is pressed into adherent contact with a finishing surface, such as a=highly polished chromium plated drum or belt, and dried thereon, and thereafter the dried coated paper is intended to separate from the drum with a surface finish which is desirably a replica of the finishing surface. A difiiculty heretofore encountered in the production of cast-surfaced mineral-coated paper is sticking of the dried and set coating to the finishing surface, resulting in marring of the coated paper surface by particlesof the dried coating which adhere to the finishing surface. Indeed, this sticking may become so extreme that the entire area of the paper in contact with the finishing surface becomes tightly bonded thereto and is only removed by long and laborious treatment. Obviously, such a sticking condition makes the process of cast coating inoperable.

Several methods have been proposed to substantially overcome this sticking of mineral coatings to the finishing surface. For example, one such method seeks to maintain on the finishing surface an invisible film, substantially less than 2000 Angstrom units in thickness, of oil or other fatty material, such substances being designated as oleaginousfilm forming materials, which are characterized as relatively water-insoluble liquids which wet the casting surface. and spread into acontinuous film, yetwill not vaporize too readily at operating temperatures. The coating on the web is intended to .adhere firmly to the casting surface until the coating has dried to a non-plastic condition and is thereafter released from the casting surface. Satisfactory results utilizing this method allegedly are obtained only by periodic application of the oleaginous mate rial directly to. the casting surface, or, preferably, application of the oleaginous compound to the casting surface by incorporation of a quantity of the oleaginous release agent in the coating composition.

Obviously, this method is subject to the objection that the required function of oleaginous material on the casting surface is necessarily dependent on, and the exact quantity thereof determined by, a skilled operator who watches the point at which the paper leaves the casting surface, and hopefully increases or decreases the amount of oleaginous material on the chromium drum and/or in the coating composition in order to avoid sticking on the one hand, or loss of gloss in the finished paper on the other, the latter condition resulting from the use of an excess of oleaginous material. Even a moderate increase in the thickness of the oleaginous film may cause a mottled appearance of the finished coated paper and may leave sufficient grease on the surface of the coated paper both to make the paper distasteful to handle and to produce Another object of this invention is to provide an improved method for continuously producing cast surfaced mineral coated paper, which method facilitates ready release of coating from a casting surface.

Another object is to provide water-soluble non-ionic surface active materials which have the property of readily effecting, separation of cast surfaced mineral coated paper from a casting surfaceon which it is dried.

It is a further object to provide such non-ionic surface active materials which are effective over a relatively wide range of concentrations.

Another object is to provide a method of the foregoing type adapted to relatively high speed production.

Numerous other objects of this invention will more fully hereinafter appear.

The sole figure of the drawing schematically illustrates one method of this invention. v t

The release agents, according to this invention, include certain water-soluble non-ionic surface active materials which are either normally liquid at room temperature, or become liquid at the operating temperature of the casting surface (which temperature varies with particular operating conditions, but normally falls in the range of 230 F.). Such agents have been found to be especially useful when added to the coagulant bath disclosed in copending application Serial No. 648,227, filed March 25, 1957 by John W. Smith, now U.S. Patent 2,950,214, and which is assigned to the same assignee as this application. According to the method therein disclosed for producing cast surfaced mineral coated paper, an aqueous mineral coating composition comprising dispersed pigments and an adhesive is applied to a paper web in predetermined quantity and uniformly distributed thereon, and the coated surface of the web while still wet is thereafter contacted with a coagulant bath whereby the adhesive component of the freshly applied mineral coating is converted into a gel, without substantial drying, in a manner so as to prevent undesirable distortion of the coating film. The gelled coating is thereafter pressed against a casting surface and dried thereon.

For example, reference is made to the accompanying drawing wherein a paper web 11 to be coated is drawn from a supply roll 10 of suitable paper base stock and is led over guide rolls 12 and 13 to pass through the apparatus in the color applying zone. The web 11 passes through the nip of the coating application rolls 14, 15 where a predetermined amount of coating suspension is applied thereto and distributed with sutficient uniformity over the web surface to give the desired weight of coating material per unit area on the web.

The coating color is fed through a suitable supply line and by suitable means to one or more discharge pipes or nozzles 23 and into the nip between rolls 15 and 24 which have the direction of rotation as indicated, the color forming a pool 25. Doctor 26, as shown, functions to maintain the pool in the nip between rolls 15 and 24 and any well known doctoring means may be employed.

The coated web is then brought with the coated side out tightly around roll 16 which dips into the coagulant and release agent bath of this invention contained in a tub 17. The coated paper 11 is then transferred by press roll 18, after the coating has been formed into a nontacky tough deformable gel, into nip 19, and thereby into contact with a heated finishing roll 20 having a smooth casting surface. The Web 11 remains in contact with casting roll 20 until the coating spontaneously releases after it has substantially completely dried and is removed by tension roll 21 to winder roll 22.

Various coating materials as described in the copending application, supra, may be employed in practicing the present'inventi'onand 'as indicated by "the formulations hereinafter 'set forth, the coating material generally comprises a mineral and an adhesive in-aqueons medium.

A color formula which has been found to function satisfactorily in the practicing of the invention is of the following compdsitionQwherein the parts by weight are taken on a dry basis:

Dow 5.12-R latex. (butadiene-styrene copolymer Di-isobutylphenoxyethoxyethyldimethylbenzyl-am moniur'nchloride,monohydrate (Hyamine 1622,

Rohm & Haas Co.) 005 Such color gives satisfactory results in the practicing of this invention when admixed with water to have a solids content of approximately 50.5%. i 1

The-following examples of color formulations which have likewise been used satisfactorily are set forth for purposes of illustration, but not of limitation; The parts by weight of these compositions are taken on a dry basis:

Example [I P rts y w i Clay (Eng i h o g cl y): 4 Calcium-carbonate I I i 42.0 Soya protein (refined) 12.0.

Arrnnonia-ZS B. (parts per 100 parts of protein) 120 Dow 512 R latex 4.0. Sodium pyrophosphaten fi '0.7'5 Calcium stearate' 0.57 Hy m e 2 i 0.05.

Examp e 1! Z "T" 'T '1"'TT'7' T-'T? 'T."'T bQ i T T' "J Ti"' T?'E'7 a h -9 Q "'7 "TT' 7T1'1T'"-ET--: -V mania-2636 (parts perlOO p ts of pro ein) 12.0 P w il eR'lat -0 od um r t n a h te. 1 In; stea et Leeann J 0.05:

xam e 1V Clay (English coating clay). Calcium. carbonate V, r p q i r-"xrr"7T"-1':--'r-r-:::- 1- z .(di yan am a s p r .0. parts of p otein) 25.0. Ammonia-26 B. (parts per 100 parts of protein) 12.0 Sodium pyrophosp'hate' 0.75 Calcium stearate 0.5 Lignasan I H 0.05

Example V Calcium Carbonate 84.0 Alphapro tein I 12.0 Ammonia- 25 B. (parts per 100 parts of protein) 180 wnne C ium n Example VI Clay (domestic coating clay) 81.0 Soya protein (refined) 12.0

Azite(dicyandiamide)(parts per parts of pron) y 25.0 Ammonia-26 B. (parts per 100 parts of protein) 15.0

As described in the copending application, supra, the conversion of the adhesive component of-the' coating'to the gel state is almost instantaneous, requiring only a fraction of a second following initial-contact with the. coagulant. 'And mixing of the release agent of this invention with the coating composition is greatly restricted," and occurs to only a minor extent. Thus,the relea's'e' agent is carried on the surface of'the gelled coating'as a liquid solution (which'also contains the coagulant salts) to the casting nip. A small quantity of this solu tion passes through the casting nip, together with thegelled coating, as a fluid film thereon, and is dried in contact with the casting surface, whereby the release agent is concentrated at the plane 'of release, and functions to provide clean separation of the cast coated web from the casting surface. Accordingly, incorporation ofthe water-soluble nonei'onie surface activerelease agents of this invention in the aforesaidcoaghlant bath insures the presence of the release 'age'ntat the point where needed to provide the desired function. Cast coated webs so prepared carry coatings-which are relatively free from contamination by release agents, the amount of such agent appearing in the cast coated paper being of the order of 0l0007 to 0101b. sa-moosq-rrrma pending on operating conditions and on the concentration" of the agent used in the coagulant bath which normally ranges from 0.125 to 5 .0% by weight, this in turn de pending on the particularrelea se agent'employedf While not wishing to be restricted thereby, it is believed that the mechanism by which such water-soluble" non-ionic surface active materials operate to provide re lease is concerned with the deposition of a very thin film of a liquid between the casting surfaceand the surface of the driedcoating, and that such a film, being of low cohesive strength, splits with one partrcrnaining'on' the paper and the other part remaining on the casting surface. According to'this mechanism, the film of re lease agent between the coating and'the' casting surface does not come into existence, until all or nearly allofxthcQ water present has been-evaporated. Thus; good contact and/or adherence of the wet, plastic coating to the casting surface is obtained, 'a condition desirable for attainment of a tr lyw ceststlrface of gloss approaching. that of the casting surface, but evaporation of' the water which sets the coating toanon-plastic state also serves unti h qoa nsha ee dried The coa ng, a ter ry-f ing, is readily, completely and cleanly separated from h s i u face. p e u ablyhe ause the p t n of the thinlayer of liq'uidfilm. deposited or formed be-. we t a i and ca ti u acev 'dfirin h n p n i ionrj -Since this invention provides for the formation of the releasing liquid film at the time and place of release from the casting surface, it is relatively free from a major limitation inherent in the use of the prior art oily or so-called oleaginous materials, in that the presence of an excess over the minimum required to provide ready release does not cause a loss of gloss in the cast-surfaced mineral coated paper, as is the case with said oleaginous materials.

In the development of this invention, it was discovered that a great number of water soluble non-ionic surfactants could be employed as suitable release agents. For example, materials such as water soluble reaction products of phenols, alcohols, higher fatty acids, amides, amines, propylene oxide, and/ or ethylene oxide were found to be especially suitable. By water soluble surfactants is meant those surfactants which are self-dispersible in water and yield non-settling suspensions or clear solutions in water. Such surfactants in the practice of this invention when incorporated with coagulating electrolyte solutions, as for example, calcium formate, retain their characteristics of solubility or suspension stability with no perceptible change.

While preferred water soluble non-ionic surfactants for the purpose of this invention are selected from the class comprising polymers of ethylene oxide and/or propylene oxide and their simple ethers, equally good results were obtained with agents selected from the following chemical classes of non-ionic surface active agents: polymers of ethylene oxide and/or propylene oxide'and their simple ethers; esters of polyoxyethylene; polyethanolamine-fatty acid condensates; polyoxyethyl ene thio ethers; polyoxyethylene phenol ethers; substituted fatty amides; and polyoxyethylene amides.

A considerable number of the non-ionic water soluble surfactants of this invention are liquids or pastes at room temperature, but as mentioned hereinbefore, some of the effective materials are normally solid at room temperature, but melt and become liquid at or below the temperature of the casting surface, so that their function cannot be distinguished from that of the products which are normally liquids at room temperature.

The invention will be more clearly understood by reference to the following examples, which serve to illustrate but not limit the scope of this invention.

In each of the examples set forth hereinafter, a typical coating composition, comprising dispersed mineral pigments and an adhesive in aqueous medium was applied to apaper web in predetermined amount and spread to a uniform, smooth film thereon, as set forth anddiagrammatically shown in the copending application, supra. The wet, coated web, without substantial drying, was then contacted on its coated side with a coagulating solution of calcium formate which also contained, one of the water soluble release agents of this invention. The web traveled to and was pressed against a highly polished chromium plated, heated casting drum, whereby a considerable portion of the coagulant and release surfactant which was carried on the surface of the web was squeezed from the surface by the action of the casting nip, which permitted only a relatively thin film of said solution to pass through on the surface of the gelled coating. Heat supplied to the interior of the drum, as by steam, evaporated the water from the gelled coating and from the layer of solution lying between the coating and the casting surface. In each case, the coated web, after reaching substantial dryness, separated easily and completely from the casting surface, and was observed to have a gloss closely approaching that of the polished casting surface. And except for the inclusion of the relatively water soluble release surfactants of this invention in the coagulating bath, the preferred procedure and apparatus used in the practice of this invention is the same as that disclosed in the referred to co -pending application, supra.

The following listing presents specific examples of commercially available water soluble, non-ionic surfactants, in the concentration set forth, which were used in the practice of this invention to efiect the desirable release as described hereinbefore.

. Concentration of Example Trade-name Composition Release Agent in Ooagulaut Solution 1 Ucon 50HB polyoxyethylene 1. 0

mouo-alkyl other. 2 fin d O. 5 3 do 0.25 4 Ucon 50HB 2000 1.0 5 o 0.5 6 Plurouic F-68 Polyoxyethylene 1. 0

ether of polyoxypropylene. 7 do do 0. 5 8 Tergitol XH polyalkylene glycol 1. 0

ether. 9 Tergitol XD. -.do 1. 0 10 Oarbowax 200 polyethylene glycol 1. 0

(M. W. 200). v 11 Oarbowax 600 polyethylene glycol 1.

(M. W. 600). 12 Carbowax 1000 polyethylene glycol 1. 0

(M. W. 1000). 13 Oarbowax 6000. polyethylene glycol 0. 5

(M. W. 6000). 14 Oarbowax 20M polyethylene glycol 0.5

(M. W. 2 000 15 lvIethoxypolyethylene methoxypolyethylene 1. 0

Glycol. glycol. 16 Polypropylene Glycol polypropylene glycol 1. 0 (1M. W. 1150 G1 1 W. i50). 1 1 1 0 17 Po yuropy ene yco p0 ypropy ene g yco (M. W. 425). (M. W. 425). 18 Ethofat 142/60 mono rod 011 fatty 1. 0

acid ester of polyoxyethylene. 19 do o 0.5 20 Ethofat 242/25 mono rosin fatty acid 1. 0

ester of polyoxyethylene. 21 Sterox GD tall oil fatty acid ester 1.0

of polyoxyethylene. 22 Nonisol 210 oleic acid ester of 5.0

polyoxyethylene. 23 Nonisol 300 stearic acid ester of 5.0

polyoxyethylene. lauric acid ester of 5. 0

polyoxyethylene. polyoxyethylene sor- 1. 0

bitan mono-oleate. 0.5 do 0.25 polyethanolarnine- 1. 0

fatty acid condensate. Alrosol B fatty alkylol amide 1. 0 condensate. Ninol 737 fatty acid alkanol 5. 0 amide. Nonic 234 polyethylene glycol 1.0

tart. dodecyl thioether. Nonic 218 do 1. 0 Nonic 260 --.-do 1.0 Polytergent G300 alkyl phenol poly- 1.0

glycol ether. 35- 0.5 36 IgepalOA 630 iso-octylphenoxypoly- 1. 0

oxycthylene ethanol. 37 Michelene DDS alkyl amido alcohol.-. 1. 0 38- 5.0 39 Michelene DLD fatty acid amide ester- 5. 0 40 Antarox G-lOO alkyl polyoxyethy; 5.0

lene ethanol amide.

All of the release agents in the above examples were found to be unaffected when used in combination with an electrolyte solution such as the electrolyte solution utilized for coagulation of the adhesive component of the coating mix. While the above stated examples were prepared in connection with a 5% calcium formate solution as the coagulant, the use of other electrolytes, such as calcium acetate, zinc acetate, calcium lactate, aluminum sulfate, and the like does not interfere with the proper functioning of the release agents of this invention.

Since the methods and products herein described are for the purpose of illustration only, it is to ire-understood that the present invention includes all modifications and- 3&291175 sii cm w ich fal when the s ore o ten-rec witha casting surface, said surfactant being liquid on said casting surface and imparting substantially complete separation of said coating from. said casting surface.

2. In the manufacture of cast-surfaced mineral coated paper, the steps comprising coagulating the coating while still mobile and fluent and deformable on the paper by direct contact with a coagulating electrolyte to form said ccating a tough, able. ge con omi nt y incorporating a water-soluble non-ionic surfactant with said coagulating electrolyte which imparts substantially complete separation of said coating from a casting surface,

said surfactant being. selected from the group consisting of water-soluble: polymers of ethylene and propylene oxide and their simple ethers, esters of polyoxyethylene, polyethanolamine-fatty acid condensates, polyoxyethylene thio ethers, polyoxyethylene phenol ethers, substituted fatty amides and polyoxyethylene amides, and thereafter bringing said coating into contact with a casting surface,

said surfactant being liquid on said casting surface and imparting substantially complete separation of said coating from said casting surface.

3. The process of producing a cast-surfaced mineral coated paper in-accordance with claim 2 wherein the surfactant consists essentially of water-soluble polymers of ethylene oxide and their simple ethers.

'4. The process of producing'a cast-surfaced mineral coated paper in accordance with claim 2 wherein the surfactant consists essentially of water-soluble polymers of ethylene oxidev and propylene oxide.

5. The process of producing aEaSt-surfaced mineral coated paperin accordancewith' claim2 wherein the surfactant consistsessentially of .watensolubleesters ofpolyoxyethylene. w

6. The process of producing a cast-surfaced mineral coated paper in accordance with claim 2 wherein the sur. faetant consists essentially of water-soluble polyoxyeth ylene phenol esters.

7. The process of producing a cast-surfaced mineralcoated paper'in accordance with claim 2 wherein the surfactant consists essentially of water-soluble p'olyoxyethy ic hexitancstcrs of at y c ds 8. In the manufacture of cast-surfaced mineral coated Pap the steps mp i coagu at n t e coating whil still mobile and fluent and deformable on the paper by d r ac with a oa ul n elec y to f rm. sai coating into a tough deformable gel, concomitantlyincorporating a n c r-soluble s rfactant. withsaid coagulating electrolyte which imparts substantially complete-separationof said coatingfrom a casting surface, said surfactant being selected from the water-soluble reaction products of phenols, alcohols, higher fatty acids, amides, aminesjmercaptans and propylene oxide respectively with ethylene oxide, andthereafter bringing said coating into contacttwith a casting surface, said surfactant being liquid on saidcasting surface and imparting sub-. standa y complete sepa ation of sa d c ating from said castina ur acc.

9 T e Pr c ss f Prod cing; ast-s rf ced mineral ated. pcri c o dan w th c a m. 8 herein. t e surfactant consists essentially ofa. wateresoluble reaction nrc u ccf. ethyle e. o ide.

19., The, P ce o producin ca t-surfa ed mineral.- qc tcdrzcrer. n ac cr aacew thclaim .8 wherein the an:-

ctant onsi s. essen al y o a a cr-so ubl rea tio product of ethylene oxide and propylene oxide 11. The process of producing a cast-surfaced mineral coated paper in accordance with claim 8 wherein the S1111. factant consists essentially of a water-soluble reaction product of ethylene oxide and alcohols.

12 The process of producing a cast-surfaced mineral coated paper in accordance with claim 8 wherein thesur: factant consists essentially of a water-soluble reaction product of ethylene oxide and fatty acids.

13. The process of producing a cast-surfaced mineral Q E 'P P I in 9 dance h l i 3 wherein he S1 1: factant consists essentially of a water-soluble reaction product of ethylene oxide, and hexitan essters. Y

14. The process of producing. a cast-surfacedmineral coated paper in accordance with claim 8 whereinthe surfactant consists essentially of a water-soluble reaction product of ethylene oxide and a phenol.

15. In the manufacture of cast-surfaced mineral coated paper, the steps comprising coagulating thecoating while still mobile and fluent and deformable on the paper by direct contact with a coagulating electrolyte to form said coating into a tough deformable gel, concomitantly in oorporating a water-solublenon-ionic surfactant with said coagulating electrolyte which imparts substantially com plete separation of said coating from a casting surface,

the concentration of said surfactant in the coagulating electrolyte being of the orderof 0.25 to 5.0%, and there: after bringing said coating into contact with a casting surface, said surfactant being liquid on said casting surface and imparting substantially complete separation of said coating from said casting surface.

16. In the manufacture of cast-surfaced mineral; coated paper, the steps comprising coagulating the coating while still mobile and fluent and deformable on the paper by direct contact with a coagulating electrolyte to form said coating. into a tough deformable gel, concomitantly in; corporating a water-soluble non-ionic surfactant withsaid coagulatingelectrolyte which imparts substantially cornpiete separation of said coating from a castingsurface, said surfactant being selected from the group consisting ofwater-soluble: polymers of ethylene and propylene oxide and their simple ethers, esters of polyoxyethylene, polyethanolamine-fatty acid condensates, polyoxyethylenc thio ethers, polyoxyethylene phenol ethers, substituted fatty amides and polyoxyethylene amides, the concern tration of said surfactant in the coagulating electrolyte being of the order of 0.25 to 5.0%, and thereafterbring-j ing said coating into contact'with a 'casting surface, said surfactant being liquid on saidcasting surface and imf parting substantially complete separation of said coating from said casting surface.

17. In the manufacture of cast-surfaced mineralcoated paper, the steps comprising coagulating the coating while still mobile. and fluentiand deformable'on the paper by direct contact with a coagulating electrolyte. to form said coating into a tough deformable gel, concomitantlyim corporatinga non-ionic water-solublesurfactant with said coagulating electrolyte which impartssubstantially complete separation of said coating from a casting surface, said surfactant being selected from the water -.soluble,reaction productslofphcnols, alcohols, higher. fatty acids, amides, amines, mercaptans and propylene oxide respectively with ethyleneoXidc, the concentration of the watersoluble reaction product in the coagulating electrolyte being of the order of 0.25 to. 5.0%, and thereafter bringing] saidcoating into contact with a casting surface, said'surfactant being liquid on said casting surface and imparting substantially complete separation of said coating from said casting surface. i

18. A cast surfaced mineral coated paper substantially identical with the product obtainable by the process of claim 1.

(References on. following. page) References Cited in the file of this patent UNITED STATES PATENTS Lunsted Apr. 6, 1954 Lunsted et a1 Sept. 20, 1955 5 Payne et a1 Jan. 10, 1956 10 Hart Nov. 6, 1956 McAuslan Dec. 4, 1956 Hart Jan. 1, 1957 Smith et a1 Jan. 7, 1958 Haas et a1. May 20, 1958 

1. IN THE MANUFACTURING OF CAST-SURFACES MINERAL COATED PAPER, THE STEP COMPRISING COAGULATING THE COATING WHILE STILL MOBILE AND FLUENT AND DEFORMABLE ON THE PAPER BY DIRECT CONTACT WITH A COAGULATING ELECTROLYTE TO FORM SAID COATING INTO A TOUGH DEFORMED GEL, CONCOMITANTLY INCORPORATING A WATER-SOLUABLE NON-IONIC SURFACTANT WITH SAID COAGULATING ELECTROLYTE WHICH IMPARTS SUBSTANTIALLY COMPLETE SEPERATION OF SAID COATONG FROM A CASTING SURFACE, AND THEREAFTER BRINGING SAID COATING INTO CONTACT WITH A CASTING SURFACE, SAID SULFACTANT BEING LIQUID ON SAID CASTING SURFACE AND IMPARTING SUBSTANTIALLY COMPLETE SEPARATION OF SAID COATING FROM SAID CASTING SURFACE. 